Electrical amplifier circuit



June 17, 1930. F. H. DRAKE 1,764,552

ELECTRICAL, AMPLIFIER CIRCUIT Filed May 4, 1928 2 Sheets-Shet 1 June 1930- F. H. DRAKE 1,764,552

ELECTRI CAL AMPLIFI ER CIRCUIT Filed May 4, 1928 2 Sheets-Sheet 2 Swatch:

WMm, V atfoznzqm Patented June 17 1930 r FREDERICK Arr. DRAKE, or BooNTomnEw JERSEY,IVASSIGN'ORPVTOY'RADIQ FREQnENoY 4 -fmeonnronrns, mooaronarnn; or BOONTQN; new gamma 'oo'RroRAmoNgoE I -"NEW JERSEY ELEczine-1on i. AMPLnHER'oinouitr a Application m'a Maya; 1928; SeriaLNo;275;17t. j a

' -'lhis invention relates to electrical circuits,

and especially to electrical amplifier circuits; "and thelike,of the typeemploying electron} or Vacuum tubesjincluding an electron emitting element or cathode; an electron rece v- -1nganode or plate, and, one or more control means Whichare ordinarily inthe nature of grids or the like] Such tube'sarecoininonly designated asaaudionsatriodes, tetrodes, and

,onthe invention-l, described and'clainied inthe copending application of Lewis M. Hull, Serial No. 207,239ifiled July 20, 1927;:mw' Patent 1 72,811; and, relates .Inore particuduce onsuppressjcertain efi'ects other thajnde siredforward repateractioni of thetube, and; adapted ,especiallyto reduce or suppress 26 'certain'effectsidue to the flow of retro activej or regenerative currents 3 arising out of capacitive coupling between the output and input circuits associated with such, a tube, this capacitive 1 coupling including particulajrly capacity between the anode and controlineans' of theftube,and capacity due ctoconn'ections and' circuits associated with the anode and) p 7 v a I or the connections to one of these coils'are rev, I p

control means of the tube.

Venti-on' showing 'its application to a threeelectrode, tube of standard type. Figurje v2 shows cascaded:-garrangementjemploying 1 a the G LTQUi t-OfFIgIIIGl. Figure 3 showsone specific embodnnent of iny lnyention asap;

tubes; Figure 'showsa modification of the r a arrangement of Figure 1.; 'Fig'ure 551s aj graphic representat on showingflcertain ef-. c fGCtSTZtIflSlZig out'of the use of ny nve'nt on 11y sofforthl The inventionisan'irnprovementl larly toanfelectrical circuit adapted to re-" pliedto a cascaded arrangementincluding a: plurali iy 0f four-electrode 0r,. doubl6-grid by connecti n g tothe negativesideof the oath: F

odeAsuitable ifC, -battery,or other means for biasing the grid, n1ay;be included; in the' input circuit and may if desired be supplied vwith bypassfcondei serCfl ora grid bias ng resistance may be arrang d in the cathode circuit, as' sfwell understood in this art. The

anode circuit of the tube, associated with the anode, vl .t'iidcathodg, F includes a coil L and resistive impedance, here shown at; It;

This resistive iinpedance may take the form ofja separate fresistanceasshownin Figure 1, .or may be e nbo'dled n' th'ecoil L ,,,as,'for

examplefbylwinding this coil 'with res'ist ance, Wire of suitable size and resistance, asis 1 shown in Figure The-resistive impedance of thisc rcul'tj nay if vdes red, be made var1-' able ,o'rladjustable in orderzto obtain thedesired degree of jresistan'ce unbalance, or bale j ZLIICG of the circuit,aswillbelater explained,

A. suitable Bf batterm-or other "source'ojf di rect current; suchfas a socket-power device or thel-lil zei nay be; lincludedin this'circuit asf l QWnj, a I1d-maybe provided with ajsuita e by-passfcondenser C if desired. The coil L5 is coupled to the, coil L in thereVeISe 93 X ersedQ so that the'niutual inductance between.

thern'is negativein sign, and is connected in 'ser-ies with a coil L and tuning condenser-TO sea e circuit inWhich the tuning condenserC 1s connected across coils L and L n series; The" coil'Lg. 1s" preferably not;

coulnedto i'eithe'r' tiiecoilL orthe coil v In'practice 'Ifrequentlyiprefer to arrange the coil Lg atright angles-tofthe coilLg so as to hair .Substantially negligible elect omagnetic; v

complies he ewi h-i h i wp e cia i of thejtuninlg"condenser maybe grounded as shown ai connection thus being i'ormed through sf ndtw f he C o o wihJQh fSilSbf he. i P ifier,f:iis necessary a co rn'rnon groundl n'e beingshown inthe"drawingsto represent this con? f nee"t'ionfi lflhe capacitiveirnpedance C is an rangedbetween the control means G andthe e is d be 1M 7 jane'tioa off the 'cbilsL apdiLg, in sucha way" as to permit partial or complete reactance'balance of the circuit to reduce efiects other than desired forward repeater action of the tube. This capacitive impedance may take the form of aphysical balancing condenser C in which case it may be variable or'adjustable as shown, or may include also', .or be solely constituted by, so-called natural or inherent capacities residing in the circuitor between the elements thereof. Theoutput terminals of the amplifier circuit are indicated at 3 and 4. Eo represents the input voltage of the amplifiercircuit (which for the purposes of the present application is measured with the tube unlighted) and'E represents the output voltage of the amplifier.. The ratio 0 therefore represents the voltage amplification, or gain, of the amplifier.

Figure 2 represents a multi-stage arrangement in which two amplifierstageseach similar to that shown in Figure '1 are arranged in cascaded relation, the tubes being designed as T and T respectively. The coupling system between these tubes includes the primary L with its associated resistive impedance, B and the tuned circuit L L C the tuning condenser C being connected directly between the grid and cathodeof the second tube. The other circuit arrangements may be substantially as before. It is of course understood that in all cascaded or mult'i-stage arrangements according to. my invention,

stage arrangement employing such tubes..

common A, B, and .C batteries may be employed for theseveral tubes, and may or may: not be provided with by-pass condensers andthe like,as required. 7 These batteries may of course be replaced by socket-power devices; the G batteries may be connected outside the tuned circuit, or may be replaced by biasing resistances; and tubes of the type employing alternating current filaments or heater cathodes, maybe employed equally.

with those, illustrated, without departing from my invention.

My invention applies equally, also, to circuits including tubes. of the four-electrode or so-called .doublegrid type. Oneor more such tubes may be employed in circuits according to my invention, and Figure 3 illustrates one specific embodiment of ajmulti-.

The tubes here illustrated areof the type designed for useaccording to the method which comprises employingthe inner grid, or that acent thecathode, as the, control element, and impart ng to the second grid a positive bias, asby @connection to the BF-battery, or

by other suitable means. the arrangement llustrated, the grids, G5, are given a] positive bias by such alconnectionto the B .-batteries,- which. are bypa'ssed condensers C. The

other circuit arrangements. may appropriately be substantially as in Figures 1, and. 2.

- n a ternative circuit arrangemen sui b f other means, in which case the coils L and L may be conductively separated by an isolating condenser, as shown in the above-mentioned copending application of Lewis M.

'Hull. My invention may also be applied to circuits including double grid tubes of the type designed for use according to the method which comprises employing thegrid G as the control element, and imparting a positive bias to the grid G 1 Figure 4- is a fragmentary diagram of an arrangementsimilar to that of Figure 1, except that the desired resistance, R is imparted to the anode circuit by the self-resistance of the coil L This may be done by winding the coil L with resistance wire. The resistance oftlie wire to be useddepen dsnpon considerations hereafter. pointed out, but I may suitably employ various commercial resistance wires for this purpose, for example, Nichrome wire. The input circuit, and connections to. the grid and cathode (not shown) may suitably be arranged as in Figure 1. a

In explaining the operation of my invention, I may state that most balanced or neutralized-circuits are designed to reduce or supressall effects except those due to forward repeater action of the tube.- Asa result, a typical completely-balanced circuit will normally yield an amplification of the desired input, or signal voltage which is determined solely by'the amplifier constants of the vacuum tubes and the constants of the associated circuits, substantially unmodified by retroactive or regenerative effects arising from the incidental fcapacitycouplings of the tube. This amplification may appropriately be termed the repeater amplification of the stage. It is'a fact well established by theory and experiment, however, that in certain types of amplifier circuits, as for instance cir cuits involving fixed inductances tuned to resonance/at difierent wavelengths by variable condensers, this repeater amplification tends to vary with frequency or wavelength, assuming large values; at the, shorter wave-- lengths and smaller-values at thelong. Wavelengths, all within the range of agiven variabletuning condenser in combination with a G by means of a separate biasing battery or overall amplification by regeneration, and

v thus produce instability, but, in" addition," to,

further modify the behavior of the stage in such a Way thatthe net amplification, at the shorterwavelengths, is even less than the repeater amplification. This tends to pro- .duce more uniform amplification over the avelength rangeto Which the stage may be Where the realization of full repeater amplifituned.-.According'to my invention'the re-Q sistanceR may serve to accomplish this purpose, 'in'addition'to providing a refinement in'the conditions of balance in other cases cation is no detriment and a 'substantiall complete one-Way balance is desired. a 7

I W ith'outlirniting my'invention to depend upon'any particular theory, I may state that I believethe fbehavior of resistance R in troduced in series with theanodecoil of the balanced circuit shownin each. of the figures tojbe as follows :The circuit may be adjusted, and is subject to reactance balance be ence of tWeen the several reactive elements includ ing the tube capacity C,,-,,"the condition for, which is specified lowing equation Where a I a r i 'T O represents inter-electrode capacity-between anode and control element of the tube,

-1. 7 1 1,1 a r i C vrepresentsflthe balancingcapacity. I ;'M represents the s mutual inductance be-f coil-L g Thisjcondition,

filled,v results ina substantial; suppression of all first order regenerative efi'ects in-th'e stagesv resistance;R in series with the anode'coil L constrains all *retroactive: input circuit. throughcapacity(L to flow alsothrough this" resistancet -Thje efiect of this is, in general, to as the circuit Lg+L 'C is tuned to-resonance, and to profil currents s returning, to i the modify the input voltage E duce either a resistance-balance betweenthe variousjfresistive elements of the: electrical network, or touprovide anon-regenerative controllederesistancennbalance in, the presill, the reactive feedback c'oniponentsare sub 7 stantiallybalancedilout iiracc'orda-nce with amplification "below'lthe I the tb0V6 equation." This resistance unbal-f be employed t'ol redu'cje theiov'eral-l repeater amplifica{ tion at "shorter iwavelengthsx since the lcur rents fedi .back invirtue fofltheiunbalan'ced resistance component in the: circuit arediss'i- 1 pative (ixeirltend 'tolredufce E5) as contrasted with "the .rcurrents which; are suppressed by thereactancebalance'because they are regene approximately by the 61;

a substantial reactance balance where closely Woundi,"

is' ofcoursej;

era'tive' (ii e. tend to increase E l have'd-is covered, that the degree of" this dissipative:

unbalance due to-the presenceof B tendsto increase "with increasing irequency, Thus,

sforexamplathe resistancelt may be soj-pro portioned as to decrease the short avelength, ainplification or gain of the amplifier circu t Without appreciably afiecting the long wave;

length amplification or gain I thereof. Alter- I natively, the' resistance Bimay be sopr'opor tioned' as to perinit the increase to a noticeable or subtantial extent of the long Wavelength amplification. or" the circuitWithout causing loss of stabilityinthe'circuit at shorter wave lengths." Thus the resistance R may be proportioned so as to-have :a I difierentialfefiect upon the amplifierv circuit',jreducing the aim plification at relatively shortwavelengths' Where excessive amplification 'is-not ordina-fl rily desired, andlleavingthe amplification-at "S5 relatively long Wavelengths substantially 1m: 1

affected. Moreover, by a proper adjustment 7 of R a substantially perfect resistancelbalanceamong the componentsofthe network may be obtained, inv addition tothe When such a resist-ancebalance isfobtained,

Gertainof the abovejdescribe'djeifects a'jri's-fv ing' from resistance unbalance various val-uesro fRi', in one particularcircuit,

curves illustrateithe relation bet-Ween nates andwavelengths plottedjas ab-sfcis'sae.

electrical i the voltage E is found;tobej sub-stantially V uni ed, f i i ii f The curves shown in'Figure 5 were taken,

tro n experimentalidata obtained with aspe-f cific circuit embodying ni'y inve'ntion. 1 The Constants of-this circuitwere a proximately I at fOHCWSg' I I v. r I

ab uxgaee Was substantiallyconstant over The foregoing constants applyto to; e fsp cific circuitenibodying niy invention, which;

consents: a

PThus, in the case of a single or nulti-stage amplifier, the stability may: bg b ta tii l yi I i;

its

the Wavelengthrange of200'tof55 mters,

jlotg limited to these 'orj-sirifila I :reactance balancethereof alreadyfdesc r'ibed:

tained, with respect to the long wavelength amplificatlonobtainable with such an amplifier having merely inherent or natural resistance in the anode-cathode circuit, without rendering the amplifier unstable at short Wavelengths. In either of these cases the action of the controlled resistance unbalance produced by the use of the resistance R results in an amplifier having substantially more constant or uniform amplification over the wavelength range over which it is designed to operate, than would be obtained 7 with the normal self-resistance of the primary coil L when wound with low resistance wire such as copper, and my invention includes all such cases in which the resistance of the primary circuit is greater than the normalself-resistance of the circuitwhenL is wound with low-resistance wire.

' In my invention the resistance R operating in one arm of the balancing network, as

described above, is not equivalent or analogous to variable plate-circuit resistors of the type which have been heretofore used in nonbalanced circuits of theprior art as volume controls, or in other ways. The operation of such resistors is toreduce the output voltage of the stage by lowering the effective polarizingvoltage on the plate. ,It is a well-known fact that such volume-control resistors, in order to be eflective, must have a minimum value of the order of several thousands of 'ohms, and are not used in connection with a balancingnetwo'rk. According to my invention, the resistance Rfiwhich is propertioned in accordance with the other elements of the balanced network, may normally have a value of the order of, say, from about 50 to 200 ohms, although the invention is not limited to this range. This resistance is, ingeneral, negligible as compared with the plate resistance of the vacuum tube, and thus has no appreciable direct eiiectupon the plate.

voltage. It servesonly to modify the input voltage as described above, throughthe medium of the currentsfiowing through the capacity G It therefore has no significance except in connection witha balancing network'ot the type described. It is tobe understood that my invention includes the production of a controlled reg-- sistance unbalance in such an electrical network as is described above, this'unbalance being otdesired degree and'character; It

includes also the production of a substantially complete resistance balance :in such an electrical network. i

' The circuit arrangements illustrated in the drawings are merely certain specific embodiments of ,my invention which is not limited thereto, but which extends to numerous variations and modifications thereof.

Claims:

1. An electrical amplifier circuit comprising, in combination, a vacuum tube including at least an anode, a cathode, and a control grid; an input circuit for said stage associated with said control grid; an anode circuit connected between said anode and cathode and including an output coil and resistive impedance in excess of the normal self-resistance of said coil; a second coil coupled to said output coil; a third coil con nected in series with said second coil but having substantially negligible electromagnetic coupling therewith; and a connection between said cathode and said third coil.

2. An electrical amplifier circuit comprising, in combination, a vacuum tube includingat least an anode, a cathode, and a control grid; an input circuit for said stage associated with said control grid; an anode circuit connected between said anode and cathode and including an output coil wound with resistance wire; a second coil coupled to said output coil; a third coil connected in series with said second coil but having substantially negligible electromagnetic coupling therewith; and a connection between said cathode and said third coil.

3. An electrical amplifier stage comprising, in combination, a vacuum tube including at least an anode, a cathode, and a control grid;an input circuit for said stage connected'to said control grid; an anode circuit connected between said anode and cathode and including an'output coupling coil and resistive impedance in excess of the normal self-resistance of the anode circuit; a second coilcoupled to said output coil in the reverse sense; athird coil connected in series with saidsecond' coil but having substantially neg ligible electromagnetic coupling therewith; a connection between said cathode and said third coil; and a'balancing capacity connected between said grid and a point between said second and third coils.

&. A balanced electrical amplifier circuit including a tube having at least an anode, a cathode, and a control grid; capacitive coupling between-said anode and control grid; a coil connectedin the anode circuit of said tube; a second coil coupled to saidfirst coil;

' a thirdicoil constituting with said second coil serially connected elements of aresonant output circuit; a balancing capacitive impedance connected between said control grid and a point lITSZLld output circuit, the ratio of said balancingfcapacitive impedance to said capacitive coupling between anode and "control grid being substantially equal Y to the ratio of the mutual inductance be tween said" second coil and saidffirst coil in the anode circuit; to the sel f i-inductance of i said third coil, to'produce a substantial reactance balance of the electrical network for currents in-said resonant output c rcuit; and. meansln the anode circuit producing resistit e-unbalance of said electrical network."

5. An electrical-circuit comprising, in combination, an'electron tubelncluding at least an anode, afcathode, anda controlmeans a coil 'jand resistive impedance associated with said anode and cathode; a second coil coupled to said first coil in the reverse sense; a third'coil having'one terminal connected to said second coil but having substantially negligibleelectromagnetic co-uplingfwith said I second coilya'connection including; capaci of the network, whereby said electrical circuit may be balanced to control elfects other than those due to desired forwardvrepeater action of said electron tube.

6. An electrical circuit comprising; in com- 'bination, an electron tube including at least an anode, a cathode, and a control means; a

coil and an adjustable resistance connected second coil coupled to said first coil; a third coil having one terminal connected to said second coil but having substantially negligible electromagnetic coupling with said second coil; a connection including capacitive impedance between said control means and the junction of said second and third coils;

- and acconnection between said cathode and t a second terminal v j of said third coil; whereby said electrical circuit maybe balanced to control eflects other than those due to desired forward repeater action of said electron tube.

7. In an amplifier stage, the combination with an electrical network including an electron tube including at least an anode, a cathode, and a control means; a coil associated with'said anode and cathode; a second coil coupled to said first coil in the reverse sense; a third coil having one terminal connected to said second coil but having substantially negligible electromagnetic coupling with said second coil; a tuning condenser connected bei tween the non-common terminals of said secend and third coils; a connection including capacitive impedance between said controlmeans and the junction of said second and third coils; and a connection between said cathode and the junction of said third coil with said tuning condenser; of resistive impedancein said anode circuit in excess of the normal self-resistance of-said coil and of an order aifecting the resistive balance of the 1n series between said anode and cathode; a

, saidfanode and cathode and i network whereby said electrical network may be balanced to control effects other than those due to desired forwardirep eater actionof said electron tube. I I

A-multi-stage electrical; amplifier cir= c-uit comprising; in combination, a plurality of electron tubes each includingat. least an anodefa cathode, and a'control electrode; an input circuit associated control electrode of the first of said elecwith the cathode and Y tron tubes; and coil and resistive impedance ineXcess of the normal self-resistance, of the 1 coil associated with the anode and cathode of said-first tube; a second coil electromagn eti cally coupled to said'first coil in the reverse sense and having one terminal connected to the control electrodeiof the second of said electron tubes; a thirdcoil having one ter-' minal connected to a second terminal of said second coil'and a second terminal connected to the cathodeof said second tube, said third coil having substantially negligible 'electro magnetic" coupling "with said second. coil a connection including capacitive impedance betweenthe junction of said second'and third coils amend I tube; a'tIuning condenser connected between said first terminal of said second'coil and said second terminal of said third coil across the control electrode and cathodeterminals of control electrode of'said first.

said secondtube and a connection to ground" common'to the cathodes-of said first and sec- Ond tubes and to the junctiono'f said tuning condensei 'and Said third" coil. I

t 9. fAn creamer amplifierx circuit compris ing, in combination, an electron tube includlng at least an anodje a cathode, and-a control means an nput"c1rcurt'assocrated w th said controlmeans;acircuit associatedwi-th? V ,105 bw lta dt tivelynegiati've'f mutual inductance. therewith; a; third coilf,

v 'ncluding a coil; a second coil coupl dit Said arranged so ast'o have efi'ec connected to said second coil having; substantially negilgi-blea eieammagaeaci .c'ou; pling therewith ;-i a balancing 'circuitinclud;

ing capacitive impedance betweensai'dfcontrol junction of said second and" means andltlfie g thirdcoi ls; a"connectionbetweensaid'cathode t I and said third coil; and means, comprising th'e' resis ti've impedance ofsaid r i 0- ciated with {said anode and cathode of said tube controlling" the resistance balance rela nla j ng. the e e e t 'saiid" electrical Ci An electrical; amplifiercircnitcomprise a i i 1. I 111g at' l'east an anode, a cathode, and a' con trol means; an input circuit, associated with I e t l, .menjsia i' w t ciat w t said anode and cathode and includinga coil; a second Coll coupled to said fi'rst coihand arsaid rangediso astojhave effectively negative mu tualinductancetherewith;a third coil con nected to said second" coil but: having subing {in combinatiomjan electron tube includstantially negligible electromagnetic coupling therewith; a connection including capacitive impedance between said control means and thejunction or said second and third coils; a connection between said cathode and said third coil; and means comprising the resistive impedance of said circuit asso ciated with said anodeand cathode of said tube for reducing the short wavelength amplification of said amplifier without substan-, tially affecting the long wavelength amplification thereof. r l

11. An electrical amplifier circuit comprising, in coinbination an electron tubeincluding at least an anode, a cathode, and a control means; an input circuit associated with said control means; acircuit associated with said anode and cathodeand including acoil; a

second coil coupled to said first coil and ar-' ranged so as to have effectively negative mutual inductance therewith; a third coil connected to said second coil but having substantially negligible electromagnetic coupling therewith; a variable condenser connected in series with said second and third coils for tuning the amplifier circuit over a band of wave lengths; a connection including capacitive impedance between said control means and the junction of said second and third coils a connection between said cathode and said third coil; and means comprising the resistive impedance of said circuit asso ciated with said anodev and cathode of said tube for maintaining the amplification of. said amplifier circuit at approximately a constant value over a predetermined range of wavelengths. i

12. .An electrical amplifier circuit comprising, in combination, an electron tube includ ing at least an anode, a cathode, and a con- ;trol means; an input. circuit associated with said control means ;a. circuit associated with said anode and cathode and including a coil; a second coil coupled to said first coil and arranged soas to have efiectively negative mutual inductance therewith; a third coil connected to said second coil but having substantially negligible electromagnetic coupl-ing therewith; a connection including a capacitive impedance between said control means and the junction of said second and third coils; and a connection between said cathode and said third coil; the resistive impedance of said circuit associated with said anode and cathode of said tubebeing of such value that the long wavelength amplification ofsaid amplifier circuit may be substantially Y increasedwith respect to that of such an amplifier circuit having merely inherent resistance in'said anode-cathode circuit with-- out rendering said amplifier circuit undesir ably unstable at short wavelengths.

13. An electrical circuit comprising, in combination, an electron tube including'at least an anode. a cathode. and a control m ans.

means; an input circuit associated with said control means; a circuit flSSOClittBd. with sa d anode and cathode and including a c011,

wound with resistance wire; a second coil coupled to said first coil and arranged so as to have effectively negative mutual induct-.

ance therewith; a third coil connected to said second coil but having substantially negligiblev electromagnetic coupling with said sec-1 V ond coil a balancing circuit including capaci:

tive impedance between said control means.- and the junction of said second and third.

7 FREDERICK H. DRAKE.

ing of such a value as to. effectively control 

